An ultrasound examination is possible at five weeks of pregnancy, but the findings are generally limited compared to later scans. Ultrasound uses sound waves to create an image, confirming that the pregnancy has implanted inside the uterus. Because the gestational structures are small, the provider focuses on a few specific initial markers of growth.
The Type of Ultrasound Used at Five Weeks
At five weeks, the developing pregnancy is extremely small and positioned deep within the pelvic cavity. Standard abdominal ultrasound is nearly impossible to use because the sound waves must travel through skin, fat, muscle, and the bladder. This distance scatters the signal too much for a clear image of the tiny structure in the uterus.
Therefore, a transvaginal ultrasound (TVUS) is necessary to obtain adequate images this early in development. This procedure involves inserting a thin, lubricated probe directly into the vagina. This allows the sound waves to travel a much shorter distance to the uterus, providing higher resolution and better detail of the small gestational structures.
The TVUS is a common and safe procedure used to identify the earliest signs of an intrauterine pregnancy. While some individuals may find the procedure slightly uncomfortable, it is not typically painful and is completed quickly. This technique routinely gathers accurate information when structures are only a few millimeters in size.
What to Expect to See at Five Weeks Gestation
The primary structure visible on a five-week scan is the Gestational Sac (GS). This fluid-filled space will house the developing embryo and appears as a small, dark, round area within the thickened lining of the uterus. The GS is usually the first sign of pregnancy seen on an ultrasound, often measuring 5 to 10 millimeters in diameter.
Inside the gestational sac, the next structure sought is the Yolk Sac (YS), which appears as a small, bright ring with a dark center. The yolk sac provides initial nourishment to the embryo and helps produce early blood cells before the placenta takes over. It typically becomes visible between five and six weeks and is an important indicator of a healthy pregnancy.
The Fetal Pole, the earliest visible form of the embryo, may or may not be seen at exactly five weeks. It is often only a tiny, linear structure beginning to form near the yolk sac. If visible, the embryo is exceptionally small, often only one to two millimeters long, making it difficult to measure accurately. The absence of a visible fetal pole at this time is a common finding and does not necessarily indicate a problem.
A Heartbeat is generally not detected at exactly five weeks, and its absence is considered normal at this stage. Cardiac activity typically begins around the end of the fifth week or early in the sixth week of pregnancy. It may appear as a subtle, rapid flicker near the fetal pole. Waiting until six or seven weeks significantly increases the likelihood of detecting a visible heartbeat.
Medical Reasons for a Very Early Scan
A five-week ultrasound is not part of routine prenatal care, but it is often ordered when a specific medical concern is present. A primary reason for an early scan is to determine the location of the pregnancy to rule out an ectopic pregnancy. An ectopic pregnancy, where the fertilized egg implants outside the uterus, is a life-threatening condition requiring immediate medical attention. Seeing the gestational sac within the uterus confirms an intrauterine pregnancy.
An early scan may also investigate symptoms such as vaginal bleeding, spotting, or pelvic pain, which can signal complications. The ultrasound helps determine the source of bleeding and assess the pregnancy status. Patients with a history of recurrent miscarriage or those who conceived through fertility treatments (like IVF) are often scanned early for close monitoring.
Another use for a five-week scan is to help date the pregnancy accurately, especially when the last menstrual period date is unknown or irregular. Measuring the gestational sac diameter provides an early estimate of gestational age. This is useful for establishing a reliable estimated due date, which can be confirmed later using the embryo’s length (Crown-Rump Length).
Interpreting Inconclusive Early Results
Results from a five-week ultrasound are often described as “uncertain” or “inconclusive” because the timing is so early in development. A slight miscalculation in gestational age, perhaps due to later ovulation, can mean the difference between seeing a yolk sac and seeing only an empty gestational sac. Even a difference of a few days can significantly alter what is visible, leading to anxiety for patients.
When the scan is inconclusive, healthcare providers rely on serial blood tests to measure human chorionic gonadotropin (hCG) levels. In a healthy early pregnancy, hCG levels should increase predictably over 48 to 72 hours. Correlating this rise with ultrasound findings helps clarify the situation. If hormone levels are rising appropriately, a lack of visible structures is usually attributed to the pregnancy being too early to visualize.
The most common course of action after an inconclusive five-week scan is to schedule a follow-up ultrasound. This repeat scan is typically performed seven to ten days later, allowing enough time for a healthy pregnancy to show significant developmental progress. Not seeing a heartbeat or a distinct fetal pole at five weeks is common, and a follow-up scan is often needed to confirm proper growth.